A CT imaging apparatus operates by acquiring multiple 2D images with a rotating imaging ensemble or gantry that has an x-ray source and an imaging sensor rotating about a fixed axis relative to the patient. CT imaging allows the reconstruction of 3D or volume images of anatomical structures of the patient. Smaller, so-called “partial” CT imaging systems allow the use of a small size x-ray field focused on a local anatomical region of interest of the patient. In dental imaging, for example, a partial CT imaging system can be used for imaging two or three teeth. The advantage of such a technique is that it limits both the x-ray dose received by the patient and the size and cost of the sensor.
For CT imaging of the human head, the axis of rotation of the gantry structure that supports the x-ray source and the sensor has to be precisely positioned on a vertical line above the region of interest on the patient. This requires that the patient be precisely positioned and constrained from movement during the imaging sequence. In dental imaging, the patient is typically positioned using support devices such as a chin rest, a forehead support, a temple support and especially a bite to position the patient's fore-teeth. The axis of rotation of the gantry moves to a preset position so that the axis corresponds to a vertical line extending above the bite. The fore-teeth then serve as the reference point. If the dentist needs to capture a CT image of a molar, for example, the axis of rotation is translated in a (xy) horizontal plane to a preset position so that it extends along a vertical line through the molar. In some embodiments, the patient is rigidly fixed in position, such as with a strap surrounding the patient's head and affixed to both edges of a forehead support.
Requirements for patient support for ear, nose, and throat (ENT) partial CT imaging differ from those for dental imaging in a number of ways. For example, for imaging temporal bones, there is no need for a bite that constrains the foreteeth. Indeed, the fore-teeth cannot be used as reference point for ENT imaging as they are too distant from the ears and temporal bones. Consequently, the patient's ears serve as useful reference points for ENT imaging.
Various apparatus have been devised for stabilizing patient position for ENT imaging, including devices that employ temporal holding members that constrain the patient's ears. U.S. Pat. No. 3,737,660 entitled “Apparatus for Taking Tomograms of Parabolically Curved Objects” to Ando et al. describes a head stabilizing device with adjustable ear rods for centering the patient's head relative to a rotational axis. U.S. Pat. No. 5,642,392 entitled “Medical Radiographic Apparatus and Patient's Head Fixing Device” to Nakano et al. describes a patient frame that is intended to fix the angle and position of the head relative to a central axis for imaging.
While these solutions may provide some measure of support for the head of the patient, they require symmetric positioning of the head of the patient and centering between ear rods, and do not provide reference positions.
There is a need for patient support apparatus for obtaining a volume image of structures within the human head, wherein the apparatus provides reference positioning for the patient relative to the imaging system.